A solar power generation device using solar cells has a parallel connection of solar battery strings, each of which is constructed by a series connection of solar battery modules having these solar cells mounted thereon in order to obtain desired power. When a solar cell mounted on a solar battery module has a failure or when electromotive force of a solar cell becomes a predetermined value or lower because sunlight is blocked, to prevent current conduction of other solar cells connected in series to this solar cell, a bypass circuit is connected in parallel for each connection unit having one or more solar cells electrically connected in series or in parallel.
A bypass diode is provided in the bypass circuit, and when a solar cell normally generates power, electromotive force of the solar cell is applied to the bypass diode as an inverse bias voltage. Accordingly, power can be taken out from the solar cell without via a bypass circuit, disabling a bypass operation of the bypass circuit and keeping the bypass diode in a blocked state.
When an abnormality such as a disconnection and a reduction of electromotive force occurs in a part of solar cells within a solar battery string and then this solar cell cannot normally generate power, a current from a normal solar cell within the solar battery string passes via the bypass diode which is in parallel with this abnormal solar cell. By bypassing this abnormal solar cell, a situation that all solar cells within the solar cell string become unusable due to the abnormality of one solar cell is prevented.
When a failure occurs in a solar cell, an original generation amount of the solar power generation device can be secured by replacing a solar battery module having the defective solar cell mounted thereon. As a method of detecting such a failure of a solar cell, a method of detecting a current conduction operation to a bypass circuit has been known.
As a method of detecting a failure of a solar cell, there is a method of comparing between output voltages of solar battery strings connected in parallel, and determining that there is an abnormality in a certain solar cell module within a solar cell string having a low output voltage (Patent Document 1).
There is a method of easily detecting a failure of a solar cell panel or an electromotive-force shortage, by providing a light emitter such as a light-emitting diode in the middle of a bypass circuit, and causing the light emitter to emit light when a current flows through the bypass circuit (Patent Document 2).
There is a method of remote-monitoring a relay operation via a communication line, by providing a current detection relay in the middle of a bypass circuit (Patent Document 3).
There is a method of providing a specific-frequency transmitting circuit in each solar battery module, and causing this circuit to superimpose a signal of a specific frequency on a power line connecting solar battery modules depending on whether a solar battery module is normally generating power (Patent Document 4). In this method, during a normal time when a voltage of a solar battery module is at or above a certain voltage, transmission of a signal of a specific frequency superimposed on a power line is enabled by causing the solar battery module to supply power to the specific-frequency transmitting circuit. When a voltage of a solar battery module becomes lower than a certain voltage due to a failure or the like, power supply to the specific-frequency transmitting circuit is stopped, thereby preventing the signal of the specific frequency to be transmitted from being superimposed on a power line. A signal separating unit takes out the signal of the specific frequency, thereby making it possible to determine presence of a failure of a solar battery module or presence of an electromotive-force shortage.
In this method, a solar battery module having a failure or electromotive-force shortage can be identified by changing for each solar battery module a transmission frequency of the specific-frequency transmitting circuit. The specific-frequency transmitting circuit can suppress the power consumption required for a transmission by performing the transmission on a periodic basis, e.g., at an interval of 30 minutes, at an interval of an hour, or at an interval of a day, instead of always transmitting the signal while solar battery modules are operating.
Patent Document 1: Japanese Patent Application Laid-open No. H08-185235
Patent Document 2: Japanese Patent Application Laid-open No. H08-97456
Patent Document 3: Japanese Patent Application Laid-open No. H09-102622
Patent Document 4: Japanese Patent Application Laid-open No. 2000-269531